Field of the Invention
The invention generally relates to turning by a machine tool, such as by a lathe with a bar feeder. The invention also relates to material or article handling and to stock pulling or pushing. In another aspect, the invention relates to performing operations and transporting, applied to a machine tool performing operations of turning or boring, and especially to accessories such as stops and grippers.
Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a machine tool such as a lathe, the typical bar stock, billet, or other workpiece, must be advanced from time to time in order to permit sequential working operations to be performed. Various manual or automated devices have been developed to perform the advancing step. One type of device is a pushing mechanism, commonly referred to as a bar feeder. These have disadvantages due to their positioning on the backside of the lathe headstock. Another type of advancing mechanism has been developed to mount or operate from the front side of the lathe collet. The front mount devices are known as bar pullers, and these mount on the tool support or turret of a lathe. On a turret lathe, the bar puller is mounted at one of the several tool stations on the turret and can be moved under manual or automated control to engage the billet, to advance it, and then to withdraw. The exact control mechanism is dependent upon the technology of the lathe. Examples of applicable types of lathe are manual, mechanically automated, and computer automated. The latter group includes numerical control (NC) lathes and computer numerical control (CNC) lathes.
In the known prior art of bar pullers, U.S. Pat. No. 4,617,847 to Schaldach is an example of a scissors-style tool, which employs two arms that cross one another like scissors blades and are joined near their midpoint by a pivot. At their back ends, the two arms are joined by a tension spring that controls the closing force between the front ends of the two arms. In use, the front ends are pushed over the side of the bar to grip it. Then the tool is moved laterally to advance the position of the bar, after which the tool is pulled off the bar from the side. This style of tool is incapable of automatic adjustment to suit different tasks, with a major limitation due to linear operation of the spring, which compromises the ability of the entire tool to open sufficiently to receive the bar, close on the received bar, and maintain required clamping force on the received bar to allow the tool to advance the bar. The relatively large scissors opening needed to receive a given bar requires great expansion of the rear spring. A spring that can expand by a large distance is not typically capable of then closing the jaws with the high force that is needed to pull the bar. Thus, this style of bar puller is unsuited for handling substantial variations in the size of the bar.
U.S. Pat. No. 4,580,470 to Buck shows another style of bar puller wherein pivots mount two rocker arms at a lateral spacing on a tool body. The front ends of the rocker arms each carry a polyurethane roller. The two rollers receive a bar stock between them by rolling around the bar from the side to a position beyond the center point of the bar. A stop pin on the body, between the rocker arms, limits how far the bar stock can enter between the rollers. The result is three point contact with the bar, consisting of the two rollers and the stop pin. Compression springs are mounted between the rear ends of the rocker arms and operate with linear expansion and contraction and urge together the front rollers to receive and grip the bar. The performance range of this tool is limited by the linear acting compression springs; and the length of the rocker arms is a corresponding limitation on the size of bar that the tool can handle for lateral advancement. These springs first have to linearly compress sufficiently to receive the bar between the rollers, next must linearly expand sufficiently to close the rollers behind the center of the bar, and finally must apply sufficient pressure through the rocker arms and rollers to grip the bar with enough force for the tool to pull the bar by lateral movement of the tool. It would be difficult for a single linearly operating spring to perform these functions adequately for reliable operation. Changing springs or selecting a new spring to accommodate a new bar size or weight would be difficult and could be subject to much wasted time due to trial-and-error.
U.S. Pat. No. 4,709,603 shows another bar puller tool by Buck. Like the prior tool, this bar puller has two elongated rocker arms that are separately mounted to a tool body on pivots at a fixed separation. Similarly, the front ends of the rocker arms each carry a polyurethane roller. As in the prior Buck patent, these rollers are laterally applied to the bar to roll around a bar to beyond center point, thereby engaging the bar between the rollers. Another common feature is that a stop screw on the body is located between the rocker arms and serves to stop entrance of the bar between the rollers at a position where the rollers have closed at slightly beyond the center point of the bar. A new feature is that the rear ends of the rocker arms are mounted on threaded screws that grossly adjust the distance between the rear ends, which oppositely adjusts the gross distance between the front ends. This adjustment is made by hand to grossly fit the tool to each size of bar by closing the front ends to slightly less than the diameter of the bar. A small, linearly acting pressure adjustment spring is in compression between the rear ends of the rocker arms and allows the front ends to open by a small amount beyond the gross adjustment to receive the bar. The small, linearly acting spring then closes the front ends around the bar stock by a small distance. Thus, as in the prior Buck patent, this bar puller achieves three point contact on the bar stock, consisting of the two rollers and the stop screw. This tool is limited in its operation by the tiny capacity of the small, pressure adjusting spring. Spring performance is a necessary function rocker arm length, which means that the rocker arms are limited to a tight range of lengths. A significant limitation of this tool is that the same small spring is applied at the length of the rocker arm to every size of bar stock, thus applying limited force for gripping different sized bars. There is little or no variability available in gripping force to accommodate different sizes of bars. The bar puller also is limited by the need to manually fit all three contact points to each different size of bar. These ad hoc manual adjustments are undesirable because they are prone to waste time and are subject to error in each adjustment. In addition, the rocker arms and small spring lack significant capacity for adjustment in performance, which means that the bar puller is difficult to adapt to a substantial variety of sizes and weights of bar stock.
U.S. Pat. No. 5,960,689 to Warren shows a bar puller that is structured somewhat similarly to Buck '603 but engages the bar by axial movement, where the tool is positioned in alignment with the axial end of the bar during bar pulling operation. The engagement is only two-point rather than three, across a diameter of the bar. As in Buck '603, two elongated rocker arms are mounted to a tool body on pivots, and a gross adjusting screw is present for closing the rocker arms to slightly less than the dimension of the bar. However, in Warren the pivots are at the rear of the rocker arms and the gross size adjusting screw is at the center of the rocker arms. The front ends of the rocker arms are jaws that each carry a spring-mounted skid that is pushed toward the other jaw by a linear spring. The pair of skids can open slightly against the linear springs when the bar is forced between the jaws. The linearly acting springs function similarly to Bucks small pressure spring to provide limited pressure in the grip of the jaws. The springs are eccentrically connected to the skids so that the skids can extend at their back ends to apply extra gripping force when the bar is pulled back from the skids, such as when the tool is pulling the bar. The limitations of this tool are similar to those discussed in connection with Buck '603.
European Patent EP1870184 to Silvennoinen shows a bar puller that substantially eliminates the usual rocker arms. Instead, this puller employs a transversely elongated tool body that is transverse to the axis of the bar stock. A core of the body houses two slides that are spring-loaded on linearly acting springs. Each slide carries an external skid. The slides are spring loaded toward the center of the tool body, thus urging the skids to a closed, central position. The tool body must be located beyond the axial end of the bar so that it can approach the bar from a lateral position, but the tool body also must be moved over the axial end of the bar into a position of axial alignment. During the lateral approach, the skids strike the side of the bar and are forced apart. The skids continue to receive the bar between them until they achieve a two-point grip along a diameter of the bar. Correspondingly, the tool body will have reached the position of axial alignment at the end of the bar. This final axial positioning of the tool body is essential because the tool body lacks any rocker arms. This bar puller is limited in capacity by the use of linear springs in the body, where the same springs must accommodate linearly opening of the skids to receive the diameter of the bar and also applying sufficient grip by linear expansion to hold the bar while the bar is pulled. This tool has the further capacity limitation set by the lack of any rocker arms, which prevents the skids from opening beyond their linear range within the length of the tool body.
The development of digital technology allows great accuracy in controlling the movement and position of the lathe turret and, hence, the movement and position of a bar puller. However, the technology can be limited by the inherent capability of the bar puller. The advances in technology that are realized, for example, in the CNC lathe, relate in part to minimizing setup time and reducing the need for tooling change out. Accordingly, the ability to use automation in advancing the workpiece is optimized when the bar puller offers improved ability to engage the workpiece under a variety of conditions. Similarly, the bar puller improves efficiency when a single bar puller can accommodate an increased range of billet sizes and when this large range of handling capacity is achieved without requiring the tool to be manually adjusted for a change in size.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the method and apparatus of this invention may comprise the following.